Because miniaturization of elements in integrated circuit electronic devices drives the industry, the width and the pitch of active regions are increasingly becoming smaller, thus, the use of traditional local oxidation of silicon (LOCOS) isolation techniques is problematic. Shallow trench isolation (STI), because it creates relatively little of the bird's beak characteristic of LOCOS, is considered to be a more viable isolation technique.
A conventional STI fabrication technique typically comprises: forming a pad oxide on an upper surface of a semiconductor substrate; forming a hardmask layer comprising nitride, such as silicon nitride, having a thickness generally greater than 600 Å, on the semiconductor substrate; forming an opening in the hardmask layer; performing anisotropic etching to form a trench in the semiconductor substrate; forming a thermal oxide liner in the trench and then filling the trench with silicon oxide as an insulating material; forming an overburden on the hardmask layer. Chemical vapor deposition (CVD) has been used extensively to deposit silicon oxide in the trench. During deposition, silicon oxide will collect on top corners of the trench, and overhangs will form at the top corners. These overhangs typically grow together faster than the trench is filled, and a void in the dielectric material filling the gap is created.
FIG. 1 illustrates a partial cross-sectional view of a STI structure 19 having a void 18. A pad oxide 12 is on a surface of a substrate 10 and a hardmask layer 14 is over the pad oxide 12. A silicon oxide 16 having the void 18 is over the substrate 10 and a portion thereof is embedded in the substrate 10. The void 18 is problematic in various respects. For example, any void 18 present in the trench fill can become a receptacle of polysilicon and/or metals during subsequent processing thereby increasing the likelihood of device instability and/or device failure.
Accordingly, what is needed is a method for fabricating an isolation structure having no void in the silicon oxide from early stage of the isolation formation.